The men were from the U.S. Exploring Expedition, known as the U.S. Ex. Ex., which had left Hampton Roads, Va., in six ships on Aug. 18, 1838, under the command of Lt. Charles Wilkes. Following the Ex. Ex.'s pioneering exploration of the coast of Antarctica, the little fleet sailed north to the Hawaiian archipelago. Their goal was to ascend Mauna Loa on the island of Hawaii and make unprecedented scientific measurements from atop the volcano.

The Ex. Ex. arrived at Hilo Bay on Dec. 9, 1840, where King Kamehameha provided a grass-thatched structure for a weather station just above a small sandy beach. While writing a book about the history of Hawaii's Mauna Loa Observatory (University of Hawaii Press, 2012), I spent many hours searching for that beach.

An archivist at the Smithsonian Institution learned of my quest and sent a copy of an unpublished U.S. Ex. Ex. chart that enabled me to quickly find the beach and the location of the weather station, which Wilkes designated Observatory 1.

On Dec. 14, 1840, Wilkes, a team from the U.S. Ex. Ex and a few hundred Hawaiian bearers left Observatory 1 for the difficult trek to the summit of Mauna Loa. The Hawaiians were not properly clothed or shod, and they abandoned the ascent and the gear they carried before the summit was reached on Dec. 22.

Wilkes and his men managed to carry all their supplies and equipment to the summit at 13,680 feet.

There they stacked lava blocks around their flimsy tents to provide protection from the wind. They then began measuring temperature, sunlight, barometric pressure, atmospheric electricity, gravity and other phenomena. Mauna Loa's climate is generally tolerable, but violent winter storms can cloak the vast mountain in twisting gray clouds loaded with snow.

On Jan. 8 and Jan. 10, 1841, Wilkes and his men experienced two such storms, which he vividly described in his memoir.

On Jan. 13, the men began the long descent back to Hilo. There they stayed six weeks, making hourly measurements like those made from Mauna Loa to document the differences in the environment at sea level and at 2.6 miles over the Pacific Ocean.

The U.S. Ex. Ex. officially ended on June 10, 1842, when the surviving ships arrived at New York harbor.

During their voyage around the world, the "scientifics" of the Ex. Ex. collected 40 tons of specimens and artifacts that eventually became many of the founding exhibits of the Smithsonian Institution.